[0001] The present invention relates to residual current devices (RCDs). More specifically,
it relates to RCDs that have a test facility which, when actuated, causes the device
to trip.
[0002] RCDs are installed for protection against certain potentially dangerous situations
arising in electrical supply installations. As shown in Figure 1, an electrical supply
installation 10 has a number of conductors 11 (typically neutral and live conductors
for single phase A.C. supplies and three live conductors or three live and one neutral
conductor for three phase A.C. supplies). The conductors 11 connect to a load circuit
12 (e.g. a domestic ring main to which appliances are connected). A known RCD 13 operates
by disconnecting the supply from the load circuit 12 when an imbalance is detected
in the current flowing in the conductors 11. This imbalance is due to current flowing
to earth indicating, for example, poor insulation or electrocution of a person.
[0003] The RCD 13 has a current transformer 4 consisting of a toroidal magnetic core surrounding
the conductors 11. A sensor coil (not shown) is wound around the core so that any
imbalance in the current flowing in the conductors 11 causes a sensor signal current
5 to be induced in the sensor coil, which current is proportional to the current imbalance.
An electronic signal processing circuit 6 analyses the sensor signal current 5 to
determine if the current imbalance is at or above a pre-set trip threshold indicative
of a potentially dangerous condition in the supply circuit. The device then trips
the circuit by providing power to an actuator 17 to actuate a switch 18 to isolate
the supply from the load circuit 12.
[0004] RCD devices are required to be fitted with a test button. Pressing the button causes
the device to trip, which allows a person to test satisfactory operation of the device.
Activation of the test button closes a contact causing a test circuit to introduce
a signal to simulate a residual current so that the whole signal path from the sensor
to the switch is included in the test. This may be achieved by the circuit shown in
Figure 2. Some of the current in one of the conductors 21a of live and neutral supply
conductors 21a, 21b flows via a resistor 22 so as to bypass the current transformer
4 when a test button is pressed to close a contact 24. There are many disadvantages
with this approach. Firstly, connection of the test circuit to the mains conductors
21a, 21b is required, which can be mechanically awkward within RCD devices. Secondly,
the apparent residual current produced is voltage dependent and also dependent on
the tolerance and stability of the resistor 22. In practice, currents much greater
than the trip threshold are induced so as to ensure tripping (typically two and a
half times, and in some cases as much as five times, the rated trip value). This tests
that the device will operate, but not that it will necessarily operate at the rated
trip value. Thirdly, no account is taken of any standing residual current already
in the circuit. In the test, the device simply adds the test residual current to any
standing residual current already present. Again this means that the test is not carried
out at the rated trip value.
[0005] The following further problems may also arise. If the device fails to trip for any
reason when the button is pressed, and the button is held down, the resistor 22 can
quickly become very hot and burn. The device may be subjected to voltage variations
in the supply. As well as affecting the accuracy of the test, high voltage pulses
that may occur between the live and neutral conductors 21a, 21b can give rise to arcing
at the contact 24. RCDs are made with different trip threshold ratings and so the
resistor 22 must be changed to suit the threshold, which is inconvenient for production.
[0006] Another known method of implementing the test function is shown in Figure 3. A magnetic
field is introduced into a core 33 of the current transformer 4. A second winding
31 is provided on the transformer core 33. The winding is placed in series with a
resistor 35 in a test circuit between the live conductor 21a and neutral conductor
21b. When the test button 23 is pressed a contact 34 closes the circuit and a test
signal current flows through the second winding 31. This will induce a current in
the sense coil 32. Typically the test signal current is much smaller than the sensor
signal current required to trip the device due to current gain in the transformer
4. A 100 turn winding mean only 1/100
th of the trip threshold current is required to produce an apparent residual current
sufficient to cause a trip. This method reduces the problem of resistor heating, but
does not overcome most of the disadvantages of the previous method, such as supply
voltage connection, inaccuracy due to standing residual current, high voltage contact
rating and resistor tolerance and stability.
[0007] Another problem associated with current transformers is that of remanence. This is
an effect where the magnetic material forming the core of the transformer becomes
magnetized. This effectively lowers its permeability and prevents it from conveying
further magnetic flux. The coupling effect of the transformer is then effectively
lost or reduced and the device becomes insensitive. Magnetisation can occur when heavy
fault currents flow and are switched off when at peak value by the tripping mechanism
leaving remanent magnetisation. When this has occurred and the device is subsequently
reset, insensitivity due to remanence means that the device may be reset when a fault
is still present in the supply circuit.
[0008] It is an aim of the present invention to provide an RCD which substantially alleviates
these problems.
[0009] According to a first aspect of the present invention there is provided a residual
current device (RCD) as defined in claim 1. In an embodiment, the device is intended
for tripping an electrical supply from a circuit to be protected when a residual current
imbalance in the circuit exceeds a predetermined threshold rating, the RCD comprising:
sense means for generating an imbalance signal representative of residual current
imbalance in the circuit;
trip means intended for tripping the residual current device when the imbalance signal
exceeds the predetermined threshold rating so as to disconnect the electrical supply
from the circuit; and
test means for increasing the imbalance signal to a level which substantially corresponds
to the predetermined threshold rating whereby a trip at said rating indicates a successful
test.
[0010] It is an advantage that the device may be tested for whether or not the RCD trips
at or near the rated value. That is, a successful test indicates that the device is
operative to trip at the intended threshold rating. An unsuccessful test is one where
the device trips when the imbalance signal is below or above the threshold, this condition
indicating that the device is not operating at its rating. The test is therefore more
rigorous and accurate than the test provided in prior art devices.
[0011] The sense means may be operative for measuring an amount of any residual current
imbalance in the circuit.
[0012] The test means may be operative for calculating a difference value corresponding
to the difference between the measured residual current imbalance and the predetermined
threshold rating. The difference value may be applied such that the increase in the
imbalance signal is substantially instantaneous. Alternatively, the testing means
may be operative to ramp up or progressively increase the imbalance signal from a
low or zero value to the predetermined threshold value. This alternative provides
for determining the level of current imbalance at whichever level the device trips.
This advantageously provides for testing whether the device trips at a level which
is less than the predetermined threshold.
[0013] In embodiments of the invention, the test means effectively introduces a simulation
residual current imbalance into the device so that the sense means senses the sum
of any residual current imbalance in the circuit being protected and the simulated
residual current.
[0014] In a preferred embodiment, the sensor means comprises a current transformer having
a sense coil, the imbalance signal being an imbalance sense current induced in the
sense coil. The means for increasing the imbalance signal may include a test coil,
wherein a test current applied to the test coil is operable for introducing the simulation
current imbalance in the form of a magnetic field in the transformer, thereby inducing
the increase in the imbalance sense current in the sense coil.
[0015] The testing means may be coupled to a processor that monitors the imbalance signal
and determines the simulation current imbalance required to increase the imbalance
signal to a level that corresponds to the rated value. It is an advantage that, if
the processor detects a current imbalance below the rated trip value (a standing current
imbalance), then it determines how much to increase the imbalance signal to reach
the level that corresponds to the rated trip value, and thereby provides a more accurate
test than the prior art devices.
[0016] The processor may include an analogue to digital converter (ADC) for converting the
current imbalance signal to a digital form, a micro-controller unit (MCU) for processing
the digital signal and for providing a digital output signal, and a digital to analogue
converter (DAC) for converting the digital output signal to an analogue test signal.
The digital processing enables the generation of a test current having a waveform
and phase profile appropriate for providing the required sum.
[0017] An advantage of synthesising a waveform for the simulation current imbalance directly
from the processor is that it is independent of the electrical supply and any variations
therein. A further advantage is that the waveform can be synthesised by the processor
based on the standing residual current determined from the imbalance signal. This
means that whatever waveform, phase angle or frequency the standing residual current
has, the processor can synthesise a simulation current imbalance waveform, which,
when added to the standing residual current waveform, ensures that the device is tested
against the rated value.
[0018] Preferably, the processor is an integrated circuit in the RCD. An integrated circuit
is an effective, low cost, space-efficient processor, which is simple to assemble
into an RCD.
[0019] According to a related aspect, that does not form part of the present invention,
there is provided a residual current device (RCD) comprising:
a current transformer for generating an imbalance sense current in a sense coil in
response to a current imbalance in an electrical supply; and
a degaussing coil for substantially removing remanence in the current transformer
by application of a degaussing signal to the degaussing coil.
[0020] The degaussing coil may be combined with a test coil forming part of a testing means
in a device according to the first aspect of the present invention as defined above.
[0021] Degaussing is a method of removing a remanent magnetic field by driving the transformer
core with an alternating field which decreases in amplitude over several cycles. Removing
remanence means that a device, which has been desensitised due to a remenant magnetic
field in the transformer core, can be resensitised and thereby reestablish the device's
sensitivity so that it will continue to function in the required manner. By degaussing
to remove remanence, the device can be re-set after a trip while ensuring that the
device will trip again within a very short time if the circuit still has a fault.
[0022] The degaussing signal may be applied to the degaussing coil under the control of
a processor. The processor may be configured to apply the decaying alternating field
at a high frequency so that the degaussing signal is not detectable by the RCD's residual
current detection system. This ensures that degaussing is achieved in a very short
time and that remanence is removed quickly when re-setting the RCD. The RCD must be
capable of tripping within a specified number of cycles of the A.C. supply and so
the high frequency degaussing signal ensures that remanence is removed in fewer than
the specified number of cycles. The high frequency degaussing also enables the processor
to be configured to control degaussing during normal operation.
[0023] Embodiments of the invention will now be described with reference to the accompanying
drawings in which:
Figure 1 is a schematic circuit diagram of a known electrical installation having
a known RCD, as hereinbefore described;
Figure 2 is a schematic circuit diagram of a known test circuit for an RCD, as hereinbefore
described;
Figure 3 is a schematic circuit diagram of another known test circuit for an RCD,
as hereinbefore described;
Figure 4 is a schematic circuit diagram of a test and degaussing circuit for an RCD
in accordance with the invention;
Figures 5, 6 and 7 are graphs showing current waveforms as may be found in an RCD
according to the invention; and
Figure 8 is a graph showing a degaussing current waveform, for use in an RCD according
to the invention.
[0024] Referring to Figure 4 a power supply installation has a live conductor 40 and a neutral
conductor 42, for supplying current from a supply to a load circuit 44. An RCD 46
includes a toroidal transformer 48 having a core 50 which surrounds the live and neutral
conductors 40, 42. A sense coil 52 and a test coil 54 are wound on the core 50. A
current induced in the sense coil 52 is supplied as an input to an electronic processor
56. A switch mechanism 58, actuated by an actuator 60 under the control of the processor
56, breaks the live and neutral conductors 40, 42 when a predetermined level of residual
current is detected.
[0025] In the electronic processor 56 the input current from the sense coil 52 flows to
a transresistance amplifier 59, having a voltage output that is linearly related to
the input current. The output voltage of the transresistance amplifier 59 is then
fed via a lowpass filter 61 (to prevent aliasing) to an analogue-to-digital converter
(ADC) 62 which outputs the voltage as a digital electronic signal. The digital signal
is fed to a micro-controller unit (MCU) 64 via a digital bus 66. The MCU 64 has an
output 68 for controlling operation of the switch actuator 60.
[0026] The RCD 46 is provided with a test button 70 for closing a contact 72 to initiate
a test under the control of the MCU 64. A digital test signal provided by the MCU
64 is fed via the bus 66 to a digital-to-analogue converter (DAC) 76, which outputs
an analogue test current to the test coil 54.
[0027] In use a current imbalance between the live and neutral conductors 40, 42, generates
a magnetic field which induces a sense current in the sense coil 52. The sense current
is amplified by the transresistance amplifier 59 and converted into a digital signal
by the ADC 62 and read by the MCU 64. If the MCU 64 determines that the current imbalance
is above the predetermined rated trip value, then a trip signal is applied to the
MCU output 68 such that the switch acuator 60 actuates the switch 58 to break the
live and neutral conductors 40, 42, and thereby interrupt electrical supply to the
load circuit 44.
[0028] The device may be tested while operational in an untripped condition. Pressing the
test button 70 closes the contact 72 and initiates the test. The MCU 64 determines
the level of the current imbalance being sensed by the sense coil 52, and calculates
the amount by which the current from the sense coil 52 must be increased for the RCD
46 to trip at its rated trip value. The calculated increase is provided by means of
the test coil 54. A test current is provided to the test coil, which generates a magnetic
field in the core 50 of the transformer 48. The magnetic field generated induces an
increase in the sense current in the sense coil 52. The MCU calculates the test current
required to test whether or not the RCD trips at the rated value.
[0029] The sense coil 52 is typically 1000 turns of wire and the test coil 54 is typically
100 turns. The current in the sense coil 52 is linearly related to the residual current
by a factor determined by the turns ratio between the electrical circuit conductors
40, 41 (the primary coil of the transformer) and the sense coil 52. Therefore, a 10mA
RMS residual current induces a 10 micro-amp RMS current in the sense coil 52 for the
1:1000 turns ratio. A working bandwidth from 20Hz to 2kHz is readily achievable and
adequate for RCD purposes. The transresistance amplifier 59 is characterized by having
low (almost zero) input impedance which is necessary to ensure the sense current is
directly related to the residual current by a fixed 1:1000 ratio over the working
bandwidth. The output of such an amplifier is a voltage linearly related to the input
current with a typical gain of 10000V/A.
[0030] The ADC 62 periodically samples the voltage and each time outputs a digital electronic
value of typically 10bits. The ADC 62 can be time multiplexed so as to also sample
the line voltage of the supply via a potential divider network 74 allowing mains frequency
to be monitored. The processor 56 measures the frequency of the residual current waveform
and the sample frequency is adjusted such that a fixed number of samples per cycle
are taken. A rate of 64 samples per cycle of the residual at 50Hz gives a sample rate
of 3200Hz, whereas at 60Hz the sample rate is 3840Hz. An algorithm executed on the
MCU 64 determines the frequency of the residual current, but in cases where it cannot
be determined (e.g. the amplitude is zero, or the signal is random, or the signal
is outside the expected range of values) then the line voltage frequency can be measured
and used.
[0031] With the residual current waveform accurately represented by digital values, it is
possible to apply digital signal processing techniques to determine various parameters
of the signal and in particular to calculate its RMS value to cause a trip if this
exceeds the set threshold rating. The digital processing is performed by the MCU 64,
which includes control circuitry, arithmetic circuitry, a read/write memory for storage
of variable values and a non-volatile read-only memory which stores an executable
software program for the whole MCU 64 to follow. Other peripheral devices not shown
are also present including power supplies, clock circuits and power-on reset circuits.
[0032] The calculation of the residual current RMS is performed over a whole number of cycles
to ensure accuracy. Ten cycles of the residual waveform is a sufficient period to
perform the calculation and since the sample frequency is adjusted to give a fixed
number of samples per cycle (say 64) then the total calculation requires 640 samples.
For a 50Hz residual current frequency this therefore takes 200mS to process 640 samples
and at 60Hz takes 167mS. In both cases tripping occurs within the time set by published
standards. The software is written into the MCU 64 at manufacture using a non-volatile
memory. The non-volatile memory also contains associated configuration data, such
as the tripping current threshold and calibration data derived from measurements taken
at manufacture.
[0033] The DAC 76 either directly outputs current or otherwise outputs voltage which can
be converted to current by a linear current-to-voltage amplifier (transconductance
amplifier) or more simply using a fixed resistor. The waveshape and amplitude of the
current signal produced by this system is controlled by the MCU 64 under software
control.
[0034] Most prior art devices drive a current of up to 2.5 times the tripping threshold
of the device using mains voltage to source a sinusoidal signal at 50 or 60Hz. This
ensures that whatever standing residual current may already be present, the test current
will swamp it and guarantee the device trips. This is effective in causing a trip
but does not really test the accuracy of the system. By driving a synthesized waveform
into the test coil 54, the test current is independent of supply voltage and does
not require a high voltage switch, since the test circuit is connected to a low voltage
MCU input.
[0035] However, in order for the test coil 52 to induce the correct RMS current in the sense
coil 52 to produce a trip, it is necessary to determine the waveform of any standing
residual current. Standing residual currents are usually caused by poor insulation
or capacitive suppressor networks often found on motors. The waveform will often be
a sinewave in phase with the mains voltage but it is possible that it could be up
to 90 degrees out of phase if leakage is purely reactive and maybe up to 180 degrees
if generating equipment is present in the load circuit. Also, non-sinusoidal residual
current waveforms are common but will almost always be repetitive at the mains frequency.
To illustrate this, consider a standing residual current as measured by the processor
56 to be 20mA RMS, then the extra apparent residual current to be induced by the test
circuit can be calculated using the following equation:-
where s is the measured standing RMS residual current,
In is the RMS trip threshold and x is the required extra apparent residual RMS to be
induced by the test circuit such that the resultant measured is equal to
In. For a device where the threshold
In is 30mA then it is necessary to drive the test coil to produce an extra 22.4mA RMS
measured residual to cause tripping. However, the equation above (which is based on
the fact that the resultant RMS of two summed signals is equal to the root of the
summed squares of the individual RMS values) assumes the following conditions
- a) that the standing residual and test current are of differing frequencies
- b) that the resultant RMS of the sum of the two signals is calculated over a long
period to achieve an accurate result.
[0036] Condition "a" can be illustrated by Figure 5 where two sinusoids of equal frequency
and phase are summed, one being of a peak amplitude of 1 unit (0.7 units RMS) and
the other of 2 units (1.4 RMS). The resultant according to the equation above is 1.6
RMS or 2.2 peak. However, it is clear in Figure 5 that the resultant is of peak amplitude
3.0 and so its RMS value is 2.1. The equation actually only holds true if the two
signals are 90° out of phase as shown in Figure 6. It would be possible to measure
the phase of a standing residual current and add the test current at an appropriate
phase to generate the required resultant but this adds considerable complexity and
does not work with all wave shapes. It is therefore evident that the RMS calculation
has a dependency on the phase between the two signals being summed and an accurate
result is only obtained if the RMS is averaged over all possible phase differences.
[0037] A simpler solution is to adhere to condition "a" and drive the test signal at a different
frequency to any standing residual current. As described above, the MCU 64 is capable
of measuring the frequency, or in some circumstances it is assumed to be the same
as the measured supply frequency. The test coil 54 can then be driven at a frequency
20 % higher or lower than the measured residual current frequency (e.g. 40 Hz if the
measured frequency is 50Hz). The resultant is shown in Figure 8. The RMS of the resultant
is found to be correct as predicted by Equation 1 above, and will in fact work for
any wave shape of standing residual current. It is also true that any wave shape for
the test signal can also be used and the use of a square wave test signal rather than
a sinusoid can be simpler to synthesise. Another way of looking at this is that the
use of different frequencies means that the dependency of the resultant RMS on phase
is lost because the two signals are added over time at all combinations of phase.
[0038] Condition "b" above, requires measurement of the resultant of the standing and induced
test current signals to be performed over a great length of time to achieve accuracy.
The tripping time at the rated threshold for most RCDs is set at 300ms maximum by
the relevant standards. Therefore, when the test button 70 is pressed the device has
about 14 mains cycles (280mS) to initiate the trip. This number of cycles does give
reasonable accuracy but improved accuracy and tripping time can be achieved with some
care. With reference to figure 7 it is evident that a beat frequency is present equal
to the difference in the frequencies of standing residual current and test current,
in this case 10Hz for a 50Hz residual current. Over the ten-cycle period shown (200mS
at 50Hz) two beats are present and it is notable that the relative phases of the three
traces are the same at the start and end of the period shown. The result is accurate
since all combinations of possible phase between the two signals have been used in
the calculation exactly twice, meaning any initial phase is irrelevant and phase dependency
is lost. A measurement period which is not a multiple of the beat period gives less
accurate results since some phase combinations are seen more times than others and
so initial phase becomes a factor in the calculated RMS of the resultant. The test
signal is calculated as a fixed percentage of the standing residual current frequency
such that over the period where a fixed number of samples are used to calculate the
resultant RMS there will be an integer multiple of cycles of the beat frequency produced
between the standing residual current and test signal frequencies.
[0039] The test current calculation must take into account the turns ratio of the sense
and test coils so that the induced current ratio is correct, as well as the wave shape
used for the test signal. Also, initial tolerances in the system can be accounted
for using calibration values stored in memory at manufacture to modify the test current
amplitude. Once the residual current frequency has been determined in the manner described
above, then on initiation of a test by operation of the test button 70 a test signal
of the calculated amplitude is driven into the test coil 54 at a frequency different
to that of the residual current 54. The measurement system will be operating normally
by continuously measuring the apparent RMS values detected in the sense coil 52 over
a fixed number of mains voltage cycles and causing a trip when necessary.
[0040] Another feature of the device is the ability to effectively counter the problem of
remanence described above. To counter this problem the remanent magnetic field in
the transformer core 50 can be removed by driving the core 50 with an alternating
field which decreases in magnitude over several cycles. This technique is called degaussing.
Such a signal can be driven into the test coil 54 to permit degaussing under software
control. It is particularly useful to perform degaussing at startup of the device
as this is when the core 50 may have been left magnetized following a fault which
caused a trip. However, periodic degaussing can be implemented during normal operation
if desired, providing it can be done quickly without effecting normal operation of
the device. If the degaussing signal frequency is much higher than the operating band
to which the residual current sensing circuit is sensitive, then the high frequency
degaussing signal will not be seen directly by the measurement system. A suitable
type of waveform is shown in Figure 8. It consists of a decaying waveform whose initial
amplitude is sufficiently high to cause magnetic saturation of the core (i.e. it cannot
become more strongly magnetized). The wave form has a peak amplitude of around 2A-turns
of the test coil 54, so for a 100 turn test coil 54 this means a current of 20mA peak
is required. The subsequent decaying waveform leaves the core less and less magnetized
after each cycle. A high frequency waveform of around 10KHz is suitable and a decay
rate of 80% per millisecond over a two-millisecond period achieves degaussing in a
short time. However, the optimum parameters of the waveform are greatly dependent
upon the dimensions and material of the toroidal core. There are no extra components
required to perform degaussing as the proposed components of the test circuit of Figure
4 are able to produce the required signal. The synthesis of the waveform is undertaken
by the MCU 64 under software control. The waveshape used need not be sinusoidal as
suggested, other shapes such as rectangular waveforms are equally effective and are
simpler to synthesize.
1. A residual current device (RCD) for protecting a circuit by tripping in response to
an imbalance signal representative of residual current imbalance in the circuit, the
RCD tripping the circuit when the imbalance signal exceeds a predetermined threshold
rating, wherein the residual current device (RCD) comprises:
sense means (52) or generating said imbalance signal;
test means (54) for introducing a simulation residual current imbalance into the device
so as to increase the imbalance signal; and
a processor (64) that monitors the imbalance signal and determines the simulation
residual current imbalance required to increase the imbalance signal to a level that
corresponds to the predetermined threshold rating so that the sense means senses the
sum of any residual current imbalance in the circuit being protected and the simulation
residual current imbalance in order to test operation of the residual current device
(RCD) against the predetermined threshold rating.
2. The device of claim 1, wherein the sense means comprises a current transformer (48)
having a sense coil (52), the imbalance signal being an imbalance sense current induced
in the sense coil.
3. The device of claim 2, wherein the test means comprises a test coil, wherein a test
current applied to the test coil (54) introduces the simulation residual current imbalance
in the form of a magnetic field in the current transformer, thereby inducing the increase
in the imbalance sense current in the sense coil.
4. The device of claim 3 wherein the test coil is further operable as a degaussing coil
for removing remanence in the current transformer by application of a degaussing signal
to the degaussing coil.
5. The device of claim 4, wherein the degaussing signal is applied to the degaussing
coil under the control of a the processor.
6. The device of claim 5 wherein the processor is configured to apply the degaussing
signal so as to drive the current transformer core with an alternating magnetic field
which decreases in amplitude over several cycles.
7. The device of claim 6, wherein the processor is configured to apply a decaying alternating
field at a high frequency so that the degaussing signal is not detectable by the residual
current device.
8. The device of claim 6 or claim 7, wherein the degaussing signal has a sinusoidal or
a rectangular waveform.
9. The device of any preceding claim, wherein the processor includes an analogue to digital
converter (ADC) for converting the current imbalance signal to a digital signal, a
micro-controller unit (MCU) for processing the digital signal and for providing a
digital output signal, and a digital to analogue converter (DAC) for converting the
digital output signal to an analogue test signal.
10. The device of claim 9, wherein the processor is operable for generation of a test
current having a waveform and phase profile appropriate for providing the required
sum.
11. The device of any preceding claim, wherein the processor determines a difference value
corresponding to the difference between the measured residual current imbalance and
the predetermined threshold rating.
12. The device of claim 11, wherein the difference value is applied such that the increase
in the imbalance signal is instantaneous.
13. The device of claim 11, wherein the test means ramps up or progressively increases
the imbalance signal from a low or zero value to the predetermined threshold rating.
14. The device of any preceding claim, wherein the processor is an integrated circuit
in the residual current device (RCD).
1. Fehlerstromschutzeinrichtung (RCD) zum Schutz eines Stromkreises durch Ausschalten
in Antwort auf ein Ungleichgewichtsignal, welches einem Reststromungleichgewicht in
dem Stromkreis entspricht, wobei die RCD den Stromkreis ausschaltet, wenn das Ungleichgewichtsignal
einen vorbestimmten Schwellenwert überschreitet, wobei die Fehlerstromschutzeinrichtung
(RCD) Folgendes umfasst:
Sensormittel (52) zur Erzeugung des besagten Ungleichgewichtsignals;
Prüfmittel (54) zur Einführung eines Simulations-Reststrom-Ungleichgewichts in die
Einrichtung, um das Ungleichgewicht zu erhöhen; und
Einen Prozessor (64), welcher das Ungleichgewichtsignal überwacht und das zur Erhöhung
des Ungleichgewichtsignals auf einen dem vorbestimmten Schwellenwert entsprechenden
Niveau nötige Simulations-Reststrom-Ungleichgewicht bestimmt, damit das Sensormittel
die Summe von jeglichem Reststromungleichgewicht in dem geschützten Stromkreis und
dem Simulations-Reststrom-Ungleichgewicht erkennt, um den Betrieb der Fehlerstromschutzeinrichtung
(RCD) dem vorbestimmten Schwellenwert gegenüber zu prüfen.
2. Einrichtung nach Anspruch 1, wobei das Sensormittel einen Stromwandler (48) mit einer
Sensorspule (52) umfasst, wobei das Ungleichgewichtsignal ein in die Sensorspule induzierter
Ungleichgewichterkennungsstrom ist.
3. Einrichtung nach Anspruch 2, wobei das Prüfmittel eine Prüfspule (54) umfasst, wobei
der der Prüfspule aufgebrachte Prüfstrom ein Simulations-Reststrom-Ungleichgewicht
in der Form eines magnetischen Feldes in den Stromwandler einführt, wodurch die Erhöhung
des Ungleichgewichterkennungsstromes in der Sensorspule induziert wird.
4. Einrichtung nach Anspruch 3, wobei die Prüfspule ferner als Entmagnetisierungsspule
betrieben werden kann, um die Remanenz in dem Stromwandler durch das Aufbringen eines
Entmagnetisierungssignals an die Entmagnetisierungsspule zu beheben.
5. Einrichtung nach Anspruch 4, wobei das Entmagnetisierungssignal der Entmagnetisierungsspule
unter der Kontrolle eines Prozessors aufgebracht wird..
6. Einrichtung nach Anspruch 5, wobei der Prozessor dazu konfiguriert ist, um das Entmagnetisierungssignal
aufzubringen, um den Stromwandlerkern mit einem magnetischen Wechselfeld, welches
über mehrere Zyklen an Amplitude abnimmt, anzutreiben.
7. Einrichtung nach Anspruch 6, wobei der Prozessor dazu konfiguriert ist, um ein zerfallendes
Wechselfeld bei einer hohen Frequenz aufzubringen, so dass das Entmagnetisierungssignal
von der Reststromeinrichtung nicht festzustellen ist.
8. Einrichtung nach Anspruch 6 oder 7, wobei das Entmagnetisierungssignal eine sinusförmige
oder rechteckige Form aufweist.
9. Einrichtung nach einem der vorangehenden Ansprüche, wobei der Prozessor einen Analog-zu-Digital-Wandler
(ADC) zur Umwandlung des Stromungleichgewichtsignals in ein digitales Signal, eine
Mikro-Kontroll-Einheit (MCU) zur Verarbeitung des digitalen Signals und zur Bereitstellung
eines Ausgangssignals und einen Digital-zu-Analog-Wandler (DAC) zur Umwandlung des
digitalen Ausgangssignals in ein analoges Prüfsignal aufweist.
10. Einrichtung nach Anspruch 9, wobei der Prozessor zur Erzeugung eines Prüfstromes mit
einer Wellenform und einem Phasenprofil, die zur Bereitstellung der nötigen Summe
geeignet sind, betrieben werden kann.
11. Einrichtung nach einem der vorangehenden Ansprüche, wobei der Prozessor einen Differenzwert,
welcher der Differenz zwischen dem gemessenen Reststromungleichgewicht und dem vorbestimmten
Schwellenwert entspricht, bestimmt.
12. Einrichtung nach Anspruch 11, wobei der Differenzwert so angebracht wird, dass die
Erhöhung des Ungleichgewichtsignals unmittelbar ist.
13. Einrichtung nach Anspruch 11, wobei das Prüfmittel das Ungleichgewichtsignal hochfährt
oder allmählich von einem niedrigen oder Null-Wert bis zu dem vorbestimmten Schwellenwert
erhöht.
14. Einrichtung nach einem der vorangehenden Ansprüche, wobei der Prozessor ein in der
Fehlerstromschutzeinrichtung (RCD) eingebauter Stromkreis ist.
1. Dispositif à courant résiduel (DCR) pour protéger un circuit par déclenchement en
réponse à un signal de déséquilibre représentant un déséquilibre de courant résiduel
dans le circuit, le DCR déclenchant le circuit lorsque le signal de déséquilibre excède
un seuil nominal prédéterminé, dans lequel le dispositif à courant résiduel (DCR)
comprend :
des moyens de détection (52) pour générer ledit signal de déséquilibre ;
des moyens d'évaluation (54) pour introduire un déséquilibre de courant résiduel de
simulation dans le dispositif de façon à augmenter le signal de déséquilibre ; et
un processeur (64) qui surveille le signal de déséquilibre et détermine le déséquilibre
de courant résiduel de simulation requis pour augmenter le signal de déséquilibre
à un niveau qui correspond au seuil nominal prédéterminé de sorte que les moyens de
détection détectent la somme de tout déséquilibre de courant résiduel dans le circuit
protégé et du déséquilibre de courant résiduel de simulation afin d'évaluer le fonctionnement
du dispositif à courant résiduel (DCR) par rapport au seuil nominal prédéterminé.
2. Dispositif selon la revendication 1, dans lequel les moyens de détection comprennent
un transformateur de courant (48) ayant une bobine de détection (52), le signal de
déséquilibre étant un courant de détection de déséquilibre induit par la bobine de
détection.
3. Dispositif selon la revendication 2, dans lequel les moyens d'évaluation comprennent
une bobine d'évaluation, dans lequel un courant d'évaluation appliqué à la bobine
d'évaluation (54) introduit le déséquilibre de courant résiduel de simulation sous
la forme d'un champ magnétique dans le transformateur de courant, induisant ainsi
l'augmentation du courant de détection de déséquilibre dans la bobine de détection.
4. Dispositif selon la revendication 3, dans lequel la bobine d'évaluation peut en outre
fonctionner comme une bobine de démagnétisation pour éliminer une rémanence dans le
transformateur de courant par application d'un signal de démagnétisation à la bobine
de démagnétisation.
5. Dispositif selon la revendication 4, dans lequel le signal de démagnétisation est
appliqué à la bobine de démagnétisation sous la commande d'un processeur.
6. Dispositif selon la revendication 5, dans lequel le processeur est configuré pour
appliquer le signal de démagnétisation de façon à entraîner le noyau de transformateur
de courant avec un champ magnétique alternatif qui diminue en amplitude sur plusieurs
cycles.
7. Dispositif selon la revendication 6, dans lequel le processeur est configuré pour
appliquer un champ alternatif décroissant à une fréquence élevée de sorte que le signal
de démagnétisation n'est pas détectable par le dispositif à courant résiduel.
8. Dispositif selon la revendication 6 ou la revendication 7, dans lequel le signal de
démagnétisation présente une forme d'onde sinusoïdale ou rectangulaire.
9. Dispositif selon l'une quelconque des revendications précédentes, dans lequel le processeur
inclut un convertisseur analogique-numérique (CAN) pour convertir le signal de déséquilibre
de courant en un signal numérique, une micro-unité de commande (MUC) pour traiter
le signal numérique et pour fournir un signal de sortie numérique, et un convertisseur
numérique-analogique (CNA) pour convertir le signal de sortie numérique en un signal
d'évaluation analogique.
10. Dispositif selon la revendication 9, dans lequel le processeur peut fonctionner pour
la génération d'un courant d'évaluation ayant une forme d'onde et un profil de phase
appropriés pour fournir la somme requise.
11. Dispositif selon l'une quelconque des revendications précédentes, dans lequel le processeur
détermine une valeur de différence correspondant à la différence entre le déséquilibre
de courant résiduel mesuré et le seuil nominal prédéterminé.
12. Dispositif selon la revendication 11, dans lequel la valeur de différence est appliquée
de sorte que l'augmentation du signal de déséquilibre soit instantanée.
13. Dispositif selon la revendication 11, dans lequel les moyens d'évaluation accélèrent
ou augmentent progressivement le signal de déséquilibre d'une valeur basse ou nulle
au seuil nominal prédéterminé.
14. Dispositif selon l'une quelconque des revendications précédentes, dans lequel le processeur
est un circuit intégré dans le dispositif à courant résiduel (DCR).